The present invention relates to a spreader driving device for a sewing machine, including a stepping motor which starts in synchronism with the elevating motion of a needle bar. The stepping motor drives a lever provided with a spreader used to perform, for example, the upper decorative stitch operation or the smock stitch operation. The spreader driven by the stepping motor can be shifted at the center of swinging motion thereof toward a suitable position corresponding to the selected stitch operation.
The present invention has been filed as Japanese Patent Application No. 2000-189417 and No. 2001-17137 with the Japanese Patent Office as an upper decorative stitching device to drive the spreader to perform an upper decorative stitch operation or a smock stitch operation by use of the stepping motor. The upper decorative stitching device is disclosed in Japanese Patent Laid-Open Gazette No. Hei 10-137474, which is a prior application by the present applicant. Also, the upper decorative stitching device provided with two spreaders has been disclosed in, for example, Japanese Patent Laid-Open Gazette No. Sho 58-138476.
The usual upper decorative stitching devices including the above-mentioned devices are divided into those of smock stitch operation and upper decorative stitch operation, which are almost constructed so as to use the predetermined stitch operation only.
The problem that the present invention is to solve is that firstly, a lever provided at the tip thereof with the spreader is driven by the stepping motor starting in synchronism with the elevating motion of a needle bar.
Secondly, the lever acting as the center of swinging motion of the spreader generates the least skip stitches corresponding to the selected stitch operation respectively and can be shifted to the most suitable position for avoiding interference with the needle and spreader.
In order to solve the above-mentioned first problem, the present invention provides a spreader driving device for a sewing machine, which is so constructed that a frame mounted to the back side of a presser foot for the sewing machine is provided with the stepping motor and the support shaft. A lever provided at the rear end thereof with a sector gear and at the fore end with the spreader is swingably fitted onto the support shaft. The sector gear of the lever engages a gear driven by an output shaft of the stepping motor, and the stepping motor operates in reciprocation with the elevating motion of a needle bar so as to swing the lever. Therefore, the spreader provided at the fore end of the lever is driven in reciprocation along the upper surface of a presser foot.
In order to solve the second problem, the present invention provides a spreader driving device which divides the frame into a movable frame provided with the stepping motor, the support shaft and the lever, and a fixed frame for mounting the device to the sewing machine. Between both the frames is arranged a shifting means for shifting the movable frame a moderate distance parallel to the needle position with respect to the fixed frame fixed at the sewing machine side for holding the fixed frame at the shifting destination. Therefore, the center of swinging motion of the spreader can be displaced corresponding to a selected stitch operation.
As mentioned above, the spreader driving device according to the present invention is made to drive the lever having the spreader at the fore end thereof by the stepping motor in synchronism with the elevating motion of a needle bar. Thus, an accurate stitch operation can be performed without generating skip stitch, and can avoid interference with the needle and spreader.
Also, the movable frame movably provided corresponding to the selected stitch operation can be shifted together with the stepping motor, the support shaft, and the lever, so that the support shaft serving as the center of swinging motion of the spreader can be shifted to the most suitable position to the stitch operation. Thus, it is further possible to perform the stitch operation without generation of skip stitch and to avoid the interference with the needle and spreader.
The device of the present invention can be constructed so that the levers provided with the sector gears respectively are fitted at two vertical stages onto the support shaft. The sector gear of one lever engages with a driving gear mounted on the output shaft of the stepping motor, the sector gear of the other lever engages with a driven gear engageable with the above-mentioned driving gear so as to mutually reversely rotate, and the stepping motor operates to drive the levers in two vertical stages to move in reciprocation in opposite directions to each other. The spreaders for the upper decorative stitch operation and smock stitch operation are exchangeably mounted onto the tips of the respective levers. The shifting means is operated to displace the support shaft in position rightwardly against the sewing machine during the upper decorative stitch operation so as to swing the upper decorative stitching spreader, and the support shaft is displaced onto the center line of needle position during the smock stitch operation so as to swing the smock stitch spreader. Thus, the center of swinging motion of the spreader is put at the most suitable position for the respective selected stitch operations.
The shifting means can comprise fixed pins which are disposed at a plurality of positions on the movable frame, and a plurality of slots are provided at the fixed frame so as to fit the respective fixed pins parallel to the needle position of the sewing machine. Presser plates bring the movable frame into close contact with the rear surface of the fixed frame and in slidably press contact with the fixed frame. A switching lever is swingably provided on the fulcrum shaft erected on the fixed frame, and fits into a slot formed at the middle portion of the lever a support pin erected on the movable frame. A toggle spring is stretched between the tip of the switching lever and one end of the movable frame so as to hold the movable frame in the upper decorative stitching position and smock stitching position. The shifting operation of the center of swinging motion of the spreader and the holding of the position in the shifting destination are easy to perform by a relatively simple construction.
A rod of proper length can be fixed at the base of one lever on the support shaft, a counter bar can be detachably connected to the tip of the rod, and a slide guide part can be provided at the movable frame along the cloth feed direction. The counter bar is slidably fitted into the slide guide part, and a thread guide for the upper decorative stitch operation is mounted onto the tip of the lever and synchronized with the swinging motion of the other lever to be longitudinally slid at the lateral side of needle position, whereby the thread feed to the spreader can be smoothed and the interference with the needle and spreader can be avoided as much as possible.